In case the domain name that you own is in use, and you are wondering if you need to point a domain, first check out should I point my existing domain name to Systeme IO.
You can point a domain you own to Systeme io, regardless of whichever domain registrar you use (e.g., Godaddy/NameCheap/BlueHost/Cloudflare/etc.).
First, go to Settings – Domains

Click on the Add Domain button.

And enter the domain name you want to use with Systeme io.

The DNS configuration will be shown. These are the settings you need to enter in your domain registrar (or wherever your domain is bought and hosted)
In essence, you need to create 2 CNAME records. Enter the first CNAME (with host 1 and value 1) followed by the second CNAME ((with host 2 and value 2). Kindly note that for the Host, you only need to enter the one underlined in red. You do not need to enter the ones without underlines.

(Important: for Value, remember to include the dot or period (.) at the end of the value. Omitting the dot will result in an error)
Configure The Host and Value in NameCheap
Regardless of the domain registrar that you are using, you can set the CNAME in your registrar.
If you’re using NameCheap, login to your account and under Domain List, click your domain. Change the Nameservers to NameCheap BasicDNS.

Click on the Advanced DNS. Click on Add New Record and that will open up a selection of available records.

Select CNAME Record

Copy the Host and Value that you got from Systeme io earlier and paste in the NameCheap CNAME record. You will need to add two CNAME records.

Redirecting domain
In addition to adding two CNAMEs earlier, you will need to add one more for redirection purposes.
If you skip this process, your website won’t be accessible when someone types yourdomain.com. This process ensures your website is accessible when someone types your website address with or without www.
In NameCheap, DNS section, first add a new CNAME record and then enter your domain in the Host ,and the first DNS as given in Systeme io (Settings – Domains – under your domain you’ve added, click on “show instructions”)
Then save the changes (click on the green tick)

Adding CNAMEs and redirecting is pretty same for other domain registrars (including Cloudflare). As a rule of thumb, look for DNS or advanced DNS.
DNS Resolve
While you are working on updating the DNS, the status of the domain you just added will be shown as pending validation. Once you have done, check back in a few hours, but do note that it may take any time from 24 – 48 hours for the domain propagation to complete.

The status will change from “Pending validation” to “Ready to use.” once the domain has propagated. If, after 48 hours and status is still showing as pending, check back to ensure you have copied and pasted the correct value. You may want also to check out “I Point A Domain From Cloudflare and Still Pending“)